Chimney cap



April 18, 1967 K. s. BASSETT 3,314,355

CHIMNEY CAP Filed July 26, 1965 INVENTOR. KENNETH SBAS'SETT ATT OENEVQUnited States Patent M 3,314,355 CHIMNEY CAP Kenneth S. Bassett, LaGrange, lnd., assignor to Motor gheel Corporation, Lansing, Mich., acorporation of bio Filed July 26, 1965, Ser. No. 474,870 Claims. (Cl.98-66) This invention relates to chimney caps of the type adapted toprevent down draft conditions in a furnace and to limit up draftconditions to an acceptable level.

It is an object of this invention to provide an improved flue cap orchimney cap which is adapted to neutralize the undesirable effects ofwind conditions on flue outlet pressure as well as to prevent entranceof rain into the illk.

Another object of the invention is to provide a chimney cap of the abovecharacter which consists of a minimum number of parts and hence iseconomical to manufacture.

In the drawings:

FIG. 1 is a perspective view of a chimney cap in accordance with theinvention.

FIG. 2 is a fragmentary view showing the manner in which the chimneycapis mounted on the chimney of a furnace over a roof which may be theroof of a mobile home.

FIG. 3 is a vertical section of the chimney cap taken on the line 33 ofFIG. 4.

FIG. 4 is a horizontal section taken along line 4-4 of FIG. 3.

The chimney cap of the invention provides a regulated draft in a furnaceand is particularly adapted for use with sealed combustion furnaces ofthe type often provided in mobile homes.

Incomplete combustion takes place in a furnace if there is anysubstantial down draft or if the up draft becomes excessive due to highwinds. Up drafts increase with increasing wind velocities unless thedraft is regulated and limited. Although draft regulating devices forinstallation on the furnaces itself are available, it is still desirableto provide a chimney cap which limits the up draft in the flue to anacceptable level and which prevents or minimizes down drafts.

The chimney cap is of generally cylindrical construction having sideopenings 12, a closed dome-shaped top 14 and an inlet 16 through whichflue gases enter the cap. Cap 10 may be mounted on a chimney in themanner shown in FIG. 2. The inlet 16 of the cap fits over flue 18 whichprojects above roof 20. Flue 18 vents gases from the furnace 22 whichmay be the furnace of a mobile home. Although the chimney cap 10 isparticularly useful in connection with sealed combustion furnaces formobile homes, it is not restricted to this particular application.

The details of the construction of chimney cap 10 are best seen in FIGS.3 and 4. The cap includes a flue pipe 26 having an imperforatecylindrical side wall with open bottom and top ends 16 and 28, the inletend -16 being outwardly flared to facilitate telescoping the pipe 26onto flue 18. A cylindrical side wall 30, also of sheet metal, encirclespipe 26 and is spaced radially from it to provide an annular passageway32 between pipe 26 and side wall 30. Openings 12 formed in side wall 30are spaced equidistantly from each other circumferentially of the sidewall. In this embodiment there are twelve of these openings.

As shown best in FIG. 3, each opening 12 is located radially outwardlyfrom flue pipe 26 and preferably the upper edge 34 of each opening 12 isflush with or slightly below the upper end 28 of pipe 26, and the loweredge 36 of each opening 12 is well down the length of pipe of FIG. 1

3,314,355 Patented Apr. 18, 1967 26. End 28 of flue pipe 26 couldterminate slightly below the upper edge 34 of opening 12 withoutdeparting from the principles of the invention, but it is characteristicof the structure of the invention to have the openings 12 wholly or verynearly wholly between the ends of the flue pipe in the axial directionof the cap. With this construction, flue pipe 26 acts as a verticalbaffle which isolates the flow of flue gases traveling upwardly thereinfrom the horizontal windstream flowing through passageway 3-2, and whichalso in cooperation with cover 14 and outer wall 30 tends to prevent thewindstream from entering the flue pipe, thus acting in a positive way tominimize down drafts.

Referring to FIG. 4, side wall 30 has vanes 40 one projecting inwardlyfrom one vertically extending edge of each opening 12 into passageway32. All the vanes 40 extend at the same angle A (FIG. 4) relative to aradial line R drawn through the axis of cap 10 and the junction of vane12 with side wall 30. Preferably angle A is about 2125 and when theradial dimension of passageway 32 is three inches, vanes 12 arepreferably about two inches in length. Vanes 40 may be inwardly bentportions of side wall 30 and the top and bottom edge 41 and 42 of eachvane 40 are axially spaced from the respectively adjacent horizontalportions of cover 14 and a bottom baflle 54 of the cap.

Vanes 40 direct air currents about flue pipe 26 in one circulardirection in passageway 32 so as to allow windstream air currents toenter the passageway on one side of the cap and leave it on the otherside of the cap without any excessive pressure drop en route. Such aflow of air is illustrated in FIG. 4 by arrows indicating air currentsentering openings '12 on the Windward side of cap 10 flowing in acounterclockwise direction in passageway 32 circ-urnferentially aroundflue pipe 26, and leaving through openings 12 on the opposite, leewardside of the cap. If the velocity of such air currents is fairly high,air flowing around the outside of the cap tends to create a low pressureregion on the leeward side of the cap. Where the air flowing throughpassageway 3-2 changes directions sharply before exiting through theopenings 12 on the leeward side, there is an increased resistance toflow. As a result, most of the pressure drop experienced by the airtraveling through cap 10 is concentrated in the zone between the pointwhere the direction of flow changes near the exit openings and theoutside region of low pressure on the leeward side of the cap. When windvelocity increases from a zero value, the pressure drop incurred by airflowing through passageway 32 increases very slowly whereas the pressuredrop increases more rapidly in said zone. This has the effect oflimiting negative pressure inside the cap and thus limiting up drafts toan acceptable value.

Top 14 of cap 10 comprises an imperforate cover having a dome 46 with aflat central portion 47, a brim 48 and a downwardly extending flange 49which slips over and may be spot welded to the upper end 50 of side wall30 to thereby completely close end 46 thereof. The annular space betweenthe bottom end 52 of side wall 30 and flue pipe 26 is closed by ahorizontal bottom baflle 5 4 which is imperforate except for a few drainholes 56 (FIG. 4) in baflie 54 to allow rain water to escape from thecap. Baflle 54 has down turned flanges 58 and 60 joined to pipe 26 andwall 30 respectively, as by spot welding.

Cover 14 acts as a batfle which cooperates with the upper end 28 of fluepipe 26 to deflect gases emitted from end 28 downwardly into passageway32 in a fountain-like path. This constructional feature allows the useof the imperforate flue pipe 26 while still providing a low resistancep-ath via passageway 32 and openings 12 for flue gases to escape fromthe flue pipe. When air cur-rents are 3 present, the flue gases join theair currents in passageway 32 and flow out the leeward side of the cap.When there are no air cur-rents, flue gases will escape from all of theopenings 12.

From the foregoing description it will now be understood that thechimney cap of the invention is inexpensive in construction and yetperforms the desired functions in a reliable manner. The cap has onlyfour parts, all of which may be easily formed from sheet metal andjoined together by, for example, spot welding, rivets or snap lockingengagement.

I claim:

1. A chimney cap comprising a flue pipe adapted to be oriented inoperative position with its axis vertical, said pipe being open at theupper and lower ends thereof and being substantially imperforate betweensaid ends thereof, a side wall spaced radially outwardly from andencircling said flue pipe adjacent the upper end thereof to define withsaid flue pipe an annular passageway radially therebetween, said sideWall being disposed with at least the major portion of its axialdimension extending downwardly from the plane of the upper end of saidflue pipe, said side wall having ciroumferentially spaced openingstherein establishing communication between said annular passageway andthe exterior of said cap, said openings having upper and lower edgesdisposed generally axially between the ends of said flue pipe, a seriesof vanes disposed one adjacent each of said openings and projecting fromsaid side wall into said passageway for directing air currents thereinin one circular direction about said flue pipe in response to windcurrents entering said passageway via the openings in the windward sideof the cap and leaving via the openings on the leeward side of the cap,a substantially int-perforate cover spaced above the upper end of saidflue pipe and closing the upper end of said side wall to form asubstantially imperforate upper baffle over the upper end of said fluepipe for directing gases leaving said flue pipe into said passageway anda substantially imperforate lower baffle extending radially between saidside wall and said flue pipe below said vanes to define a bottom wall ofsaid annular passageway.

2. The chimney cap of claim 1 in which said side wall consists of acylindrical piece of sheet metal and said vanes are portions of saidpiece bent inwardly thereof from axially extending edges of saidopenings, the upper and lower edges of said vanes and said openingsbeing axially spaced respectively below and above the upper and loweredges of said side wall such that two imperforate bands of metal remainin said side wall, one above and one below said openings.

3. The chimney cap of claim 1 in which said vanes each extend atsubstantially the same angle with respect to an imaginary radial linedrawn through the axis of said pipe and the junction of the associatedvane with said side wall.

4. The chimney cap of claim 1 in which said upper end of said flue pipeand the upper end of each of said openings are flush with one another.

5. The chimney cap as set forth in claim 1 wherein said side wall iscylindrical and concentric with said flue pipe and each said vaneextends from said side wall at an angle of about 21 to about 25 withrespect to an imaginary radial line drawn through the axis of said fluepipe and the junction of said vane with said side wall.

References Cited by the Examiner UNITED STATES PATENTS 918,962 4/ 1909Cauchemount 9866 2,717,547 9/1955 Grenzebach et al 9866- FOREIGN PATENTS894,908 10/ 1953 Germany.

ROBERT A. OLEARY, Primary Examiner.

M. A. ANTONAKAS, Assistant Examiner.

1. A CHIMNEY CAP COMPRISING A FLUE PIPE ADAPTED TO BE ORIENTED INOPERATIVE POSITION WITH ITS AXIS VERTICAL, SAID PIPE BEING OPEN AT THEUPPER AND LOWER ENDS THEREOF AND BEING SUBSTANTIALLY IMPERFORATE BETWEENSAID ENDS THEREOF, A SIDE WALL SPACED RADIALLY OUTWARDLY FROM ANDENCIRCLING SAID FLUE PIPE ADJACENT THE UPPER END THEREOF TO DEFINE WITHSAID FLUE PIPE AN ANNULAR PASSAGEWAY RADIALLY THEREBETWEEN, SAID SIDEWALL BEING DISPOSED WITH AT LEAST THE MAJOR PORTION OF ITS AXIALDIMENSION EXTENDING DOWNWARDLY FROM THE PLANE OF THE UPPER END OF SAIDFLUE PIPE, SAID SIDE WALL HAVING CIRCUMFERENTIALLY SPACED OPENINGSTHEREIN ESTABLISHING COMMUNICATION BETWEEN SAID ANNULAR PASSAGEWAY ANDTHE EXTERIOR OF SAID CAP, SAID OPENINGS HAVING UPPER AND LOWER EDGESDISPOSED GENERALLY AXIALLY BETWEEN THE ENDS OF SAID FLUE PIPE, A SERIESOF VANES DISPOSED ONE ADJACENT EACH OF SAID OPENINGS AND PROJECTING FROMSAID SIDE WALL INTO SAID PASSAGEWAY FOR DIRECTING AIR CURRENTS THEREININ ONE CIRCULAR DIRECTION ABOUT SAID FLUE PIPE IN RESPONSE TO WINDCURRENTS ENTERING SAID PASSAGEWAY VIA THE OPENINGS IN THE WINDWARD SIDEOF THE CAP AND LEAVING VIA THE OPENINGS ON THE LEEWARD SIDE OF THE CAP,A SUBSTANTIALLY IMPERFORATE COVER SPACED ABOVE THE UPPER END OF SAIDFLUE PIPE AND CLOSING THE UPPER END OF SAID SIDE WALL TO FORM ASUBSTANTIALLY IMPERFORATE UPPER BAFFLE OVER THE UPPER END OF SAID FLUEPIPE FOR DIRECTING GASES LEAVING SAID FLUE PIPE INTO SAID PASSAGEWAY ANDA SUBSTANTIALLY IMPERFORATE LOWER BAFFLE EXTENDING RADIALLY BETWEEN SAIDSIDE WALL AND SAID FLUE PIPE BELOW SAID VANES TO DEFINE A BOTTOM WALL OFSAID ANNULAR PASSAGEWAY.